First detach the claws with the joints from the trunk with a twisting motion.
Then, using a large kitchen knife, pierce lengthwise between the head and the trunk and cut the lobster in half lengthwise.
Remove the green liver and stomach sac with a small spoon. Carefully remove the intestines from the tail meat with a small knife or tweezers.
Gently tap the large claw piece all around with the back of the knife without damaging the claw meat.
Gently move the scissor fingers backward and forward a few times, loosening them and releasing them slightly, but do not pull them completely off the scissor finger meat.
Sauté the carcass and shell scraps briefly in butter with some finely diced root vegetables and pour in fish stock and reduce to one-third.
Then pour the stock through a sieve, heat again and thicken with some cornstarch dissolved in water.
Season to taste with sea salt and white pepper, remove from heat, add crème fraîche and keep warm again (do not boil).
Wash or brush the potatoes well with skin, cut into finger-thick sticks. Place in cold water for 30 minutes and then pat dry well.
Fry in hot fat at 140° C just until they are slightly yellow. In the second deep fry at 190°C until they float on top and are golden crisp. Drain on paper towels and lightly salt with fine sea salt.